The invention relates to a sealing system for media-carrying parts according to the preamble of claim 1.
In order to meet the increased demands made as regards hygiene and product quality, such as e.g. the reduction in the quantity of preservatives in cosmetic products and foods, the increase in the keeping quality of dairy products and beverages, as well as in the pharmaceutical and other industries, where GMP (Good Manufacturing Practice) is a prerequisite, corresponding installations, components and parts are required, which satisfy the requirements as regards low germ content and sterility.
It has been found that in particular the sealing system of the components or the like is a key aspect of such processes. As a result of ageing phenomena, external influences such as temperature, attacks by aggressive media, the seals are often damaged to such an extent that at the seal zone between the components dead volumes, clearances, etc. form, which are potential contamination sources, so that it is possible for germs, bacteria or the like to be deposited there. Thus, the nature of the seal is particularly critical. Whereas on the one hand a profile seal has been discussed, other users favour a sealing system using an O-ring.
The problem of the invention is to provide a detachable sealing system for media-carrying parts, which differs from conventional seals in that it has a better sealing action and consequently satisfies the constantly increasing demands made in low-germ or sterile processes.
This problem is solved by the features of claim 1. Further developments of the invention form the subject matter of the subclaims.
The invention proposes that the media-carrying parts have precisely complimentary sealing surfaces to one another and which are directly pressed against one another for forming a clearance-free seal. The contact surface between the sealing surfaces is limited to a narrow area directly adjacent to the media area. Unlike in the case of conventional seals, the sealing system according to the invention has no additional sealing element, such as a sealing ring or the like. Preferably it is a purely xe2x80x9cmetal on metal sealxe2x80x9d made from the same basic material and whose sealing action is brought about by the characteristically formed sealing surfaces on both parts, when the latter are braced against one another. A surface treatment or coating is possible, but not absolutely necessary. The complimentary sealing surfaces act in the manner of a plug and a die, which engage in one another. As opposed to conventional seals, where as a result of the material thickness of the sealing element a clearance always forms towards the media area, the seal in the present case is free from clearances. In particular the sealing clearances on conventional seals constitute potential contamination sources, because the sealing element can deform through the clearance into the media area, where a bead-like projection forms, on which residues in the form of puddles can e.g. form on emptying media-carrying pipelines and which constitute an ideal nutrient medium for bacteria or germs. This problem is obviated by the clearance-free seal of the connection according to the invention. In general, the sealing elements of conventional seals are foreign bodies, which behave quite differently to the remaining media-carrying parts. They are e.g. permanently exposed to the medium, e.g. gases or liquids and can consequently be attacked or swell, which leads to a reduction in the sealing action. They are also exposed to constant temperature changes, e.g. if the installation is steam-sterilized. For example, conventional sealing rings are only allowed up to approximately 135xc2x0 C. in low-germ or sterile processes. However, in the process according to the invention the seal is formed by the media-carrying parts, so that a swelling or the like is impossible.
Another advantage of the sealing system requiring no elastomeric seals is that in the case of thermal sterilization the seal does not act as an insulator and the sterilization heat in the minimum time reaches all necessary areas by heat conduction.
Media-carrying parts in the sense of the present application are understood to be all devices in contact with or conveying media, such as liquids or gases and which can be devices in the form of pipes, containers, fittings, valves, etc. The connections for media-carrying parts are understood to mean connections between the pipes, containers, etc. The sealing system can be a joint connection between two pipes, a pipe and a container, etc. Such connections can be screw, flange, clamp or clip connections or the like. However, it is also possible to use the sealing system for valves or the like, e.g. as a valve housing seal and/or as a spindle seal.
The contact surface between the sealing surfaces of the parts is limited to an area, whose size is very small compared with the nominal width of the sealing system. The nominal width is the internal diameter of the medium area of the sealing system in millimeters and which is bounded by the medium area wall. The width of the contact surface can be a {fraction (1/5,000)} to {fraction (1/50)}, preferably {fraction (1/1,000)} to {fraction (1/250)} of the nominal width of the sealing system, e.g. 0.01 to 1 mm, preferably 0.05 to 0.2 mm. This area is directly adjacent to the media area and the sealing action of the seal consequently starts directly at the transition between the contact surface and the media area.
As a result of the small dimensions of the contact surface the specific sealing pressure on pressing together the parts, is preferably in the elastic deformation range of the material of the parts. It can be close to the yield point (0.2% yield strength) of the material of the parts, e.g. 20 to 80% of the yield point value. The sealing pressure value can be approximately 30 to 140 Newton/mm2. There is no cold welding of the parts, even under a high contact pressure. However, certain plastic deformations, e.g. in parts of the surfaces are possible.
According to a further development of the invention the sealing surfaces can have a guide, which acts transversely to the media area, e.g. in the radial direction. As a guide, particularly in the radial direction, are preferably provided the profiled sealing surfaces of the parts. For this purpose the cross-sections of the sealing surfaces preferably have a complimentary curved profile. The profiles can e.g. be in the form of a bead and groove. However, preferably these sealing surfaces have two complimentary S-shaped profiles engaging in one another on bracing the parts. It is also possible to use interengaging trapezoidal profiles. The sealing surfaces can consequently form a type of ring spherical seal.
In a further development of the invention the sealing surfaces can be designed in such a way that the specific sealing pressure decreases from the intersection line of the sealing gap with the wall of the media area. This makes it possible to prevent the sealing gap xe2x80x9cbeakingxe2x80x9d at said intersection line leading to the formation of a clearance in which germs or bacteria could collect. As a result of the adjustable contour of the sealing surfaces it is possible to interchange parts without leaks occurring. In particular, an addition of tolerances in the dimensions of the sealing surfaces does not give rise to leaks. The sealing gap is always directly tight at its intersection line with the media area. The sealing surfaces are constructed as a type of sealing lip with a complimentary half-recess.
Adjacent to the contact surface formed by the two sealing surfaces can be surface portions of both parts cut free from the contact surface, which i.e. are not in stop form on bracing the parts. However, these can serve as reserve contact surfaces, if the contact surface is enlarged away from the media area under the sealing pressure. Therefore the free-cut away from the contact surface should gradually increase. These surface portions are also preferably constructed complimentary to one another. They can pass into two plane-parallel surfaces, but preferably are also curved and preferably form an annular clearance. The width of the annular clearance can e.g. be {fraction (1/5,000)} to {fraction (1/500)}, particularly {fraction (3/5,000)} to {fraction (7/5,000)} of the nominal width of the sealing system.
In a further development of the invention guide portions can be provided transversely and spaced from the sealing surfaces for the precentring of the two parts. The guide portions can e.g. be axially directed guide surfaces. At the two guide portions, particularly at the transition of the guide portions into the surface areas forming the reserve contact surfaces and at an end opposite the same, said guide portions can have insertion bevels, which are used for bringing together the two parts. The insertion bevels can e.g. be formed by chamfers. Between the two guide portions there is preferably a guide clearance, e.g. an axial separating gap, which makes it possible to orient the two parts in accurately fitting manner with respect to one another on pressing together the sealing surfaces.
In particularly preferred manner the dimension of the contact surface, particularly the sealing lip adjacent to the media area with its complimentary half-recess is dimensioned in such a way that the sealing chamfer at the transition to the media area wall is aligned in projection-free manner therewith. As a result of the clearance-free seal between aligned wall portions a detachable connection is possible, whose sealing gap is scarcely visible or tangible in the media area. Apart from ideal conditions for a low line resistance, a residue-free cleaning and emptying are possible.
According to a further development of the invention a clearance is formed between the parts in the bracing direction. The clearance is in particular so large that on bracing the sealing system up to the closing of the clearance, the sealing pressure is built up by the elastic deformation of the parts. The clearance width can be approximately {fraction (1/5,000)} to {fraction (1/100)}, preferably {fraction (1/100)} to {fraction (3/100)} of the nominal width of the sealing system. For this purpose between the sealing surface and a bracing or clamping device bringing about the bracing of the parts, e.g. tightening screws, clamps, etc. can be provided a portion of the parts, e.g. a ring or tube-like projection, which is elastically deformable. Therefore the presetting of the contact pressure is essentially determined by the size of the clearance, the length of the projection, the modulus of elasticity of the material and the flexibility of the parts.
The sealing system can also be a flange connection, in which the contact pressure is produced by screwing the flanges. Sealing systems constructed as joint connections are preferably welded in a pipeline or to a container, orbital welding being particularly suitable. The weld point is preferably approximately 35 to 50 mm from the sealing surfaces of the sealing system. This is sufficient to prevent a temperature-deformation at the sealing surfaces. In addition, the relatively large diameter and the relatively high thermal capacitance inhibits heat conduction to the sealing surface. Particularly for high-grade sealing systems the heat conduction from the weld point in the direction of the sealing surfaces is low, because the high-grade steel acts as an insulator.
The clearance-free seal can be used for the connection of two pipe or container parts. However, it can also be used for sealing valve components, e.g. for sealing a metal valve bellows.
The parts forming the sealing system and the sealing surfaces can be made from a hard material, e.g. stainless steel. However, other materials are also suitable from which all the parts can be produced, e.g. ceramic or plastics materials.
The invention also covers a process for the production of a sealing system according to one of the claims 1 to 12. The process is characterized in that the sealing surfaces can be produced by precision profile turning by means of complimentary profile cutting edges or bits. The reserve sealing surfaces can be produced at the same time using the same profile bits. The turning method can e.g. be face-turning, in which a surface located perpendicular to the workpiece rotation axis can be worked.
Plastic sealing systems are preferably produced by injection moulding. The relatively small sealing surfaces can either be moulded at the same time through the use of precision injection moulding processes or can be made subsequently by precision working.
These and further features can be gathered from the claims, description and drawings and the individual features, both singly and in subcombinations, can be implemented in an embodiment of the invention and in other fields and can represent advantageous, independently protectable constructions, for which protection is claimed here. The subdivision of the application into individual sections and the subheadings in no way restrict the general validity of the statements made thereunder.